/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkPositionIndex;

import com.google.common.annotations.GwtCompatible;

import java.util.ListIterator;
import java.util.NoSuchElementException;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * This class provides a skeletal implementation of the {@link ListIterator} interface across a
 * fixed number of elements that may be retrieved by position. It does not support {@link #remove},
 * {@link #set}, or {@link #add}.
 *
 * @author Jared Levy
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
abstract class AbstractIndexedListIterator<E extends @Nullable Object>
        extends UnmodifiableListIterator<E>
{
    private final int size;
    private int position;

    /**
     * Returns the element with the specified index. This method is called by {@link #next()}.
     */
    @ParametricNullness
    protected abstract E get(int index);

    /**
     * Constructs an iterator across a sequence of the given size whose initial position is 0. That
     * is, the first call to {@link #next()} will return the first element (or throw {@link
     * NoSuchElementException} if {@code size} is zero).
     *
     * @throws IllegalArgumentException if {@code size} is negative
     */
    protected AbstractIndexedListIterator(int size)
    {
        this(size, 0);
    }

    /**
     * Constructs an iterator across a sequence of the given size with the given initial position.
     * That is, the first call to {@link #nextIndex()} will return {@code position}, and the first
     * call to {@link #next()} will return the element at that index, if available. Calls to {@link
     * #previous()} can retrieve the preceding {@code position} elements.
     *
     * @throws IndexOutOfBoundsException if {@code position} is negative or is greater than {@code
     *                                   size}
     * @throws IllegalArgumentException  if {@code size} is negative
     */
    protected AbstractIndexedListIterator(int size, int position)
    {
        checkPositionIndex(position, size);
        this.size = size;
        this.position = position;
    }

    @Override
    public final boolean hasNext()
    {
        return position < size;
    }

    @Override
    @ParametricNullness
    public final E next()
    {
        if (!hasNext())
        {
            throw new NoSuchElementException();
        }
        return get(position++);
    }

    @Override
    public final int nextIndex()
    {
        return position;
    }

    @Override
    public final boolean hasPrevious()
    {
        return position > 0;
    }

    @Override
    @ParametricNullness
    public final E previous()
    {
        if (!hasPrevious())
        {
            throw new NoSuchElementException();
        }
        return get(--position);
    }

    @Override
    public final int previousIndex()
    {
        return position - 1;
    }
}
